Losartan, the first orally active angiotensin II receptor antagonist, has demonstrated transient uricosuric activity in man. More profound drug-induced uricosuria has previously been associated with crystalluria, increased stone risk, and acute uric acid nephropathy. This study will assess the potential for urinary crystal formation in patients with asymptomatic thiazide-induced hyperuricemia upon addition of antihypertensive doses of losartan.